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W32 
opy 1 



THE INFLUENCE 



OP 



OUR NORTHEEN FORESTS 



ON 



Til IISSISSIPPI llfll. 



BY 



S. WATERHOUSE, 



OF 



^WASHIT^iOXOBi LTHJIVERSITV. 



St Louis, Marcli 1. l«9li> 



The Importance of our Northern Woodlands 
to the Navigation of the Mississippi. 



If the water that now flows in the Mississippi were 
contracted into a narrow channel, it would, even in 
mid-summer, be amply sufficient for all the purposes 
of navigation. But anj^ material reduction in the 
volume of water would seriously increase the diffi- 
culties which now confront the Government engi- 
neers. If the axe of the northern woodsman is low- 
ering the Mississippi and its upper tributaries. Con- 
gress ought at once to enact forestry laws that will 
effectively protect those woodlands which are still 
under the national control. That the felling of large 
forests affects the distribution of the rainfall both 
reason and observation seem to prove. 

As long as the present constitution of nature exists, 
the moisture ceaselessly carried into the air by the 
process of evaporation must return to the earth. 
Does the presence or absence of trees make any dif- 
ference in the quantity of rain that falls in a given 
district? The range of comparative observation has 
been too limited for science at present to give a def- 
inite response to this inquiry. But it seems reason- 
able to believe that the chill of evaporation tends to 
condense the humidity of the atmosphere and again 
to slake the thirst of the trees with the water trans- 
pired from their leaves, or wind-borne from distant 
sources. It is well known that the functions of both 
animal and vegetable life develop electricity, and it 
is highly probable that the growth of plants produces 
electrical conditions that favor precipitation. This 
is consistent with the infinite wisdom which cosmic 
processes everywhere exhibit. It would be strange 
indeed, if nature, which makes such marvelously in- 
genious provisions to preserve the life of all the rest 
of its children, should neglect its vegetable offspring. 



The geographies studied in my childhood asserted 
that it never rained in Egypt. During the first day 
of my visit to that land, there were two showers. 
They fell in the neighborhood of the Suez Canal. But 
the quantity of water in that canal was altogether 
too insignificant to account for the result. Apart 
from the construction of this great waterway, there 
have been for ages no physical changes except the 
recent growth of a large number of trees and the 
cultivation of limited tracts on the banks of the ca- 
nal. It would appear to be a legitimate inference 
that the showers were due to the trees and the til- 
lage. It is a proverb among farmers that the clear- 
ing of woodlands causes those springs that are not 
fed from remote sources to dry up. In New England, 
some of the streams that fifty years ago were large 
enough to drive mills have, since the removal of the 
neighboring woods, dM'indled to mere brooklets. 
The deforesture of northern Maine has heightened 
the spring freshets and lowered the mid-summer 
flow of the rivers. Many streams that were once 
deep enough to float logs to the mills have become 
too shallow for the lumbermen to use. It is said that 
the waters of our great northern lakes are gradually 
sinking. 

There is no apparent explanation of this subsi- 
dence, except the wide-spread destruction of for- 
ests around the sources of the tributary rivers. 
The rains pass off in sudden floods, and do not, by 
slow filtration through the soil, maintain the level of 
the lakes by a relatively steady and evenly distrib- 
uted inflow. 

It has been stated that the rain-gauge shows that 
there is no greater amount of precipitation on wooded 
than on bare lands. If the same showers pass over 
both tracts, the statement is probably true; but it is 
my belief that, in the case of large sections, the for- 
ests are more frequently watered than the prairie. 

But grant that the precipitation is the same in 
both instances. What follows ? It is necessary to 



- 5 - 

trace merely the results of the rainfall in the sum - 
mer season, for that is the time when low water em- 
barrasses navigation; and to speak only of large 
areas, for small ones would not exert a perceptible 
influence on the climate. 

The soil of the northwest, in which the Mississippi 
has its sources, is largely a clayey loam. When it is 
unprotected by the shade of trees, the heat of a 
summer sun bakes the surface into a hard crust. 
Unless the rains are protracted, and they seldom are 
in the warm months, they fail to soften the crust 
and penetrate deeply into the soil. If the surface 
is uneven, most of the water flows quickly into the 
streams and is borne away from that region. If the 
surface is level, the intense heat causes rapid evap- 
oration. Moreover the radiation of a large body of 
heated land rarefies the air and creates thirsty winds 
which greedily absorb moisture. In consequence of 
the rapid off-flow and evaporation, comparatively 
little water is stored in the soil of an unwooded 
district. 

But lands shaded by forests are not sun-scorched. 
The ground remains friable. Most of the rain is 
absorbed into the porous earth. Unless the showers 
are very heavy, the immediate flow into the streams 
is relatively small. 

The cool forests do not engender hot winds, but 
break those which come from the open plains; the 
trees ward off the solar heat with their leafy shields; 
and the exhalation of moisture from the foliage 
lowers the temperature of the woodland. All of 
these conditions tend to check evaporation from the 
soil. A large part of the humidity of forest-clad 
grounds passes into the air by transpiration, but the 
woodlands, even after they have satisfied the in- 
temperance of the trees, contain a greater quantity 
of moisture than that which shadeless and sun-dried 
fields absorb; and this water, slowly percolating 
through the earth, feeds the springs and maintains 
the rivers. 



- 6 - 

Doubtless tillage tends to counteract the bad effects 
of cutting forests. The plow, the cultivator, and 
the shade serve^to keep the soil mellow, and the 
rains would sink deep into the earth. In the com- 
parison of crops with woods, evaporation would be 
greater, and transpiration less; for even the most 
luxuriant maize would not break the force of hot 
winds as effectively as trees would, while the extent 
of the cereal leafage would-be far less than that of 
the sylvan foliage. If it is true that, since the co- 
lonial times, there has been no material decrease in 
the rainfall of New England, the fact is unquestion- 
ably attributable to a cultivation which is nearly 
coextensive with the cleared lands. But this condi- 
tion of general tillage does not prevail in the remote 
northwest. In that almost uninhabited region, 
there is scarcely one cultivated acre to the square 
mile. Consequently the plowed clearings are too 
limited perceptibly to counteract the injurious ef- 
fects of felling the forests. 

In a brief discussion of the climatic conditions 
which affect the stage of water in the Mississippi, it 
is quite unnecessary to advert to the influence which 
mountain ranges, ii'respective of woods, exert upon 
precipitation, inasmuch as there are no mountains 
near the sources of the Mississippi. 

With an equality of conditions in area, t<'mper- 
ature, friability, and rainfall, it seems probable that 
there would be a greater exhalation of moisture from 
the cleared than from wood land. There is less 
evaporation in the shade than in the ojjcn air; and 
the trees only exhale the water which comes to their 
roots by the mysterious process of diffusion. 

In the densest forest, the roots occupy onlj^ a 
small portion of the ground, but diffusion is active 
among all the atoms of the soil. It would certainly 
seem that the free evaporation from the whole sur- 
face of the ground would be more rapid than trans- 
piration through foliage of moisture drawn from 
relatively limited spaces. Under the assumed con- 



ditions, unless the absorbent force of capillary at- 
traction is vastly greater than the diffusive energy 
of the soil, the amounts of transpiration and evapo- 
ration would approximately correspond to the pro- 
portion that subsists between the areas of the roots 
and of the given tract. 

Even in the most respectable and civilized cli- 
mates, there are surprising instances of misbehav- 
ior. Turbulent cyclones create tumults in the most 
peaceful and best ordered states of the atmosphere* 
But, though there are apparent exceptions to the 
normal action of the elements which it baffles the 
present efforts of science to explain, these un- 
common phenomena do not at all impair our confi- 
dence in the general stability of natural laws. The 
constanc}' with which nature provides for the wants 
of vegetable life would seem to justify the belief 
that the showers which refresh the woodlands are 
more frequent than those that water the open plains. 
But it is certain that, even if the forests do not in- 
crease the rainfall, they at all events insure its slow 
and useful distribution. This is a highlj^ important 
fact which statesmen desirous of improving the nav- 
igability of the Mississippi river cannot afford to ig- 
nore. The importance of the subject invites the grave 
consideration of our national legislators. If more 
stringent forestry laws would at all serve to maintain 
the volume of the Mississippi, then Congress would 
be faithless to its duty, if it failed to enact them. 
A judicious preservation of northern woodlands 
might perhaps prevent the expenditure of additional 
millions in deepening the channel of the river. The 
improvement of the Mississippi is now a sufficiently 
arduous undertaking, without the increased diffi- 
culties with which a still lower stage of water would 
invest the problem. 



mSZj'' CONGRESS 

iiiill 

014 497 2™0'i 



i 



LIBRARY OF CONGRESS 



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014 497 274 



